Hi Zenghui,
On 23/04/2020 12:57, Zenghui Yu wrote:
> On 2020/4/23 19:35, James Morse wrote:
>> On 22/04/2020 17:18, Marc Zyngier wrote:
>>> From: Zenghui Yu <yuzenghui@xxxxxxxxxx>
>>>
>>> It's likely that the vcpu fails to handle all virtual interrupts if
>>> userspace decides to destroy it, leaving the pending ones stay in the
>>> ap_list. If the un-handled one is a LPI, its vgic_irq structure will
>>> be eventually leaked because of an extra refcount increment in
>>> vgic_queue_irq_unlock().
>>
>>> diff --git a/virt/kvm/arm/vgic/vgic-init.c b/virt/kvm/arm/vgic/vgic-init.c
>>> index a963b9d766b73..53ec9b9d9bc43 100644
>>> --- a/virt/kvm/arm/vgic/vgic-init.c
>>> +++ b/virt/kvm/arm/vgic/vgic-init.c
>>> @@ -348,6 +348,12 @@ void kvm_vgic_vcpu_destroy(struct kvm_vcpu *vcpu)
>>> {
>>> struct vgic_cpu *vgic_cpu = &vcpu->arch.vgic_cpu;
>>> + /*
>>> + * Retire all pending LPIs on this vcpu anyway as we're
>>> + * going to destroy it.
>>> + */
>>
>> Looking at the other caller, do we need something like:
>> | if (vgic_cpu->lpis_enabled)
>>
>> ?
>
> If LPIs are disabled at redistributor level, yes there should be no
> pending LPIs in the ap_list. But I'm not sure how can the following
> use-after-free BUG be triggered.
>
>>
>>> + vgic_flush_pending_lpis(vcpu);
>>> +
>>
>> Otherwise, I get this on a gic-v2 machine!:
>
> I don't have a gic-v2 one and thus can't reproduce it :-(
>
>> [ 1742.187139] BUG: KASAN: use-after-free in vgic_flush_pending_lpis+0x250/0x2c0
>> [ 1742.194302] Read of size 8 at addr ffff0008e1bf1f28 by task qemu-system-aar/542
>> [ 1742.203140] CPU: 2 PID: 542 Comm: qemu-system-aar Not tainted
>> 5.7.0-rc2-00006-g4fb0f7bb0e27 #2
>> [ 1742.211780] Hardware name: ARM LTD ARM Juno Development Platform/ARM Juno Development
>> Platform, BIOS EDK II Jul 30 2018
>> [ 1742.222596] Call trace:
>> [ 1742.225059] dump_backtrace+0x0/0x328
>> [ 1742.228738] show_stack+0x18/0x28
>> [ 1742.232071] dump_stack+0x134/0x1b0
>> [ 1742.235578] print_address_description.isra.0+0x6c/0x350
>> [ 1742.240910] __kasan_report+0x10c/0x180
>> [ 1742.244763] kasan_report+0x4c/0x68
>> [ 1742.248268] __asan_report_load8_noabort+0x30/0x48
>> [ 1742.253081] vgic_flush_pending_lpis+0x250/0x2c0
>
> Could you please show the result of
>
> ./scripts/faddr2line vmlinux vgic_flush_pending_lpis+0x250/0x2c0
>
> on your setup?
vgic_flush_pending_lpis+0x250/0x2c0:
vgic_flush_pending_lpis at arch/arm64/kvm/../../../virt/kvm/arm/vgic/vgic.c:159
Which is:
| list_for_each_entry_safe(irq, tmp, &vgic_cpu->ap_list_head, ap_list) {
I think this confirms Marc's view of the KASAN splat.
>> With that:
>> Reviewed-by: James Morse <james.morse@xxxxxxx>
>
> Thanks a lot!
Heh, it looks like I had the wrong end of the stick with this... I wrongly assumed calling
this on gicv2 would go using structures that held something else.
Thanks,
James
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